Refrigerator evaporator with defroster-heater



Aug. 13, 1957 REFRIGERATOR EVAPORATOR WITH DEFROSTER-HEATER Filed July 27, 1956 E. C. SIMMONS 3 Sheets-Sheet l IN V EN TOR.

50 WARD C5/MM0N5 A TTOENE Y Aug. 13, 1957 E. c. SIMMONS 2,802,345

REFRIGERATOR EVAPORATOR WITH DEFROSTER-HEATER Filed July 27, 1956 3 Sheets-Sheet 3 H 7 I INVENTOR.

fpwnzp C. SIMMONS A TJ'ORNE Y United States Patent REFRIGERATOR EVAPORATOR WITH DEFROSTER-HEATER Edward C. Simmons, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application Jul 27, 1956, Serial No. 600,530

16 Claims. c1. 62-126) This invention relates to refrigeration and more particularly to an arrangement of a defroster-heater on an evaporator of a household refrigerator.

I am aware of the fact that many electrically energized defroster-heater arrangements installed on or in association with an evaporator of a refrigerating system have heretofore been proposed to impart heat to the evaporator in order to melt an accumulator of frost or ice from walls thereof. Such defroster-heater installations on an evaporator have been complicated and diflicult to install thusincreasing the cost of providing ev-aporators with a defrosting means. This is more particularly true with theme of sheet metal evaporators wherein refrigerant ducts are formed in or as an integral part of the metal sheet or sheets thereof. For this reason I contemplate the installation of a simpledefroster-heater including an electric resistance wire 'on an evaporator of a refrigerating'isystemwhich can be readily performed in an inexpensive manner and in a minimum amount of time.

An object of my'invention is to provide a low cost, improved electric defroster-heater installation on an evaporator of a refrigerating system.

Anotherobject of my invention is to provide, in an improved defroster heater evaporator combination, a flexible heater of strip form which may be easily applied, in excellent heat transfer relationship, directly to wall surfacesof a sheet metal evaporator, for supplying heat uniformly throughout the wall surfaces for defrosting purposes so as to avoid localized hot spots.

Still another object of my invention'is to provide a defroster-heater for an evaporator of a refrigerating system which compriseswa flexibleelectrical resistance wire carried in a pocket formed in a readily and easily bendable metal strip,-'a flat portion of which contacts walls of the evaporator andforms a continuous integral heat dissipating fin on the defroster-heater for increasing the transfer of heat therefrom to the evaporator.

A further and more specific object of my invention is to provide a defroster-heater comprising a flexible metal strip having aflat fin portion and sheath portions, the latter portions of which partially or substantially surround and protect a flexibleinsulated electrical resistance wire and which defroster-heater isspirally wound in one direction around opposed walls of a box-like sheet metal evaporator substantially from end to end thereof so as to be in metal. to metal contact with flat walled surfaces of refrigerant ducts in walls of the evaporator.

In carrying out the foregoing objects it is an additional objectof my invention toispirally coil a defrostenheater around opposed walls of an evaporator and to fasten the ends only of the coiled heater to the evaporator to thereby prevent unwinding of the heater therefrom and to eliminate the necessityof employing a plurality of retaining clips intermediate ends of the heater.

Furthernobjects andadvantages of the present invention will be apparentfrom the following description, reference being hadto the accompanying drawings, wherein preferred form ofthe present invention is clearly shown.

In the drawings:

Figure 1 is a front view of a household refrigerator cabinet with the door open showing an evaporator of a refrigerating system mounted in the food storage compartment thereof;

Figure 2 is an enlarged fragmentary vertical sectional view through the refrigerator cabinet taken on the line 2-2. of Figure 1 showing a defroster-heater of the present invention on the evaporator;

Figure 3 is an enlarged vertical sectional view through the evaporator removed from the food compartment of the refrigerator cabinet and showing a defroster-heater coiled around walls of the evaporator;

Figure 4 is a top view of the evaporator and defrosterheater combination of the present invention showing ends of the coiled heater fastened to the evaporator;

Figure 5 is a broken view of a long metal strip having an electrical heater resistance wire assembled thereto in accordance with my invention;

Figure 6 is an enlarged sectional view taken on the line 6--6 of Figure 4 showing means for fastening one end of the coiled defroster-heater to the evaporator;

Figure 7 is an enlarged sectional view taken on the line 77 of Figure 4 showing means for fastening the other end of the coiled defroster-heater to the evaporator;

Figure 8 is an enlarged fragmentary sectional view taken on the line 8--8 of Figure 4 showing a portion of a clamp of one of the fastening means;

Figure 9 is an enlarged fragmentary sectional view taken on the line '9--9 of Figure 4 showing another portion of the clamp of said one fastening means; and

Figure 10 is an enlarged fragmentary sectional view taken on the line 10-10 of Figure 4 showing part of the clamping means illustrated in Figure 6.

Before proceeding with the description of the invention it is desired to point out that the present disclosure is illustrated without regard to the appearance of the evaporator of a refrigerating system since the evaporator may be enclosed in or surrounded by insulating material to form a freezing chamber in a multiple compartmented refrigerator cabinet as is now common practice in the art. It is also desired to set forth that advantages of the present invention reside in the fact that the defrosterheater herein disclosed applies heat uniformly over substantially all wall portions of the evaporator and eliminates large gaps between extensions of the heater, it can be readily and quickly applied to the evaporator in close relationship since the flexibility of the heater assures surface contact regardless of irregularities in wall surfaces of the evaporator and it can be installed by spirally coiling same about sheet metal evaporators without regard to the refrigerant evaporating circulatory system or ducts provided in walls thereof. By virtue of the substantially flat strip retainer for the electric resistance wire of the defroster-heater the flat portion thereof serves as dissipating fin means for conducting heat from the partially enclosed insulated resistance wire to walls of the evaporator. Also by spirally wrapping or coiling the defroster-heater about the evaporator ends only of the heater need be fastened thereto and this eliminates the use of a plurality of securing clips or clamps throughout its length along walls of the evaporator. These advantages and the subject matter of the appended claims represent an improvement in the art over the defroster-heater disclosed in my copending application Serial No. 554,207 filed December 20, 1955 and entitled, Refrigerating Apparatus.

Referring now to the drawings I show in Figure 1 thereof a refrigerating apparatus including a cabinet 10 having a plurality of insulated walls forming a food storage chamber 11 therein provided with a door 12. Chamber 11 is provided with the usual vertically spaced .apart food supporting shelves and has an evaporator 14 of a closed refrigerating system (not shown) associated with the cabinet mounted in the upper part of the chamber, in any suitable or conventional manner, for cooling and causing circulation of air therein. A drip tray or receptacle 13 is disposed on the uppermost food shelf beneath evaporator 14 and is adapted to catch and collect water from the evaporator upon defrosting same. Evaporator 14 is substantially of box-like shape to provide walls of a freezing compartment 15 for containingtrays of water to be frozen or for the storage of frozen foods. Compartment 15 may, if desired, be provided with a shelf or shelves above thebottom wall of evaporator 14. Evaporator 14 is of the sheet metal variety and includes metal sheets which are braced to one another or preferably roll-forged together and made in accordance with the method disclosed in the Long Patent No. 2,662,273 and the Simmons Patent 2,740,188, assigned to the assignee of the present application. The flat brazed to one another or roll-forged together metal sheets of the evaporator 14 are bent preferably along four spaced apart lines to provide the top, bottom and sides of a box-like structure and a metal plate 16 is thereafter secured thereto to provide the back wall of compartment 15. A door 17 is then pivotally mounted upon evaporator 14 at the front of compartment 15 and provides access to the interior thereof. Evaporator 14 includes a plurality of substantially fiat walled refrigerant expansion ducts 18 for conveying the refrigerant about or around walls thereof so as to remove heat from compartment 15 and from air within chamber 11. The ducts 18 may lead from a refrigerant feeding manifold extending across the bottom wall of evaporator 14 and may converge into or terminate in a refrigerant outlet manifold extending across the top wall of the evaporator. These manifolds are provided with a liquid refrigerant inlet connection and a gaseous refrigerant connection respectively with conduits of the refrigeration system as is conventional in the art. The evaporator element 14 in chilling the air in chamber 11 causes moisture to be withdrawn from the air and deposited on walls of the evaporator in the form of frost or ice. When this frost accumulates or reaches a predetermined thickness it reduces the cooling effect of the evaporator and decreases the efficiency of the refrigerating system. Thus it is necessary to occasionally interrupt operation of the refrigerating system and to defrost or melt the frost and ice from the walls of the evaporator 14 and my invention is therefore particularly directed to a defroster-heater and evaporator combination.

The defroster-heater herein disclosed comprises a long substantially flat flexible metal strip 21 (see Figure 5) which has its edges rolled over as at 22 to partially surround and form a sheath for an insulated electrical resistance wire 23. The insulation 20 surrounding wire 23 is heat and water resistant and is of good thermal conductivity as compared to relatively poor heat conductive insulating material. The strip 21 is preformed from relatively soft pliable aluminum and a length of the wire 23 is placed in side pockets provided by the rolled over edges 22 of the strip. The length of wire 23 when assembled to strip 21 is of a long substantially U-shaped form with the ends 24 and 26 of legs of the U terminating short of one end of the metal strip and with the bight portion of the U curved or looped as at 27 from one side pocket to the other at the opposite end of strip 21. A suitable water-proof connection of the ends 24 and 26 of resistance wire 23 is made with heavier insulated conductor wires 28 and 29 respectively (see Figure 5). This connection is preferably located within the pockets of the rolled over edges 22 of strip 21 so as to be covered and shielded by portions of the strip. The conductor wires 28 and 29 are connected to suitable electric power lines through a switch (not shown) which may control the energization and deenergization of resistance wire 23 of the defroster-heater. The control switch may be manually operated but is preferably operated by a timer or chronometric device as is now conventional in the art to automatically and periodically stop operation of the refrigerating system and to energize the defrosterheater. The fiat portion of strip 21 of the defrost-heater extends tangentially away from its rolled over edges and is provided with spaced apart apertures or holes 31 along its length for purposes to be presently described. The manner in which the fiat portion extends from rolled over edges of strip 21 provides the same with integral heat dissipating fin means. Strips 21 with the wire 23 and conductor wires 28 and 29 in place within the pockets or rolled over sheaths of the strip are usually stored in rolls so as to minimize the space occupied thereby and to facilitate handling thereof.

In order to assemble the defroster-heater upon evaporator 14 the evaporator may be removably located upon a form which is both rotatable and advanceable laterally relative to a rolled strip 21 by a suitable lathe or the like. A strip 21 may be partially unwound from a roll thereof and its one end held against a wall of the evaporator 14 preferably at the top wall thereof. The lathe is then operated to rotate the evaporator whereupon the flexible heater strip is bent around corners of the evaporator as the same is advanced or moved laterally with respect to the rolled strip. This spirally wraps or coils the defroster-heater substantially from end to end of the evaporator 14 with the flat portion of the strip 21, intermediate its rolled over edges 22, in firm metal to metal contact with walls of the evaporator and particularly in contact with the flat walled surfaces of the refrigerant ducts 18. The defroster-heater is of a predetermined length with respect to the size of a box-like evaporator to which it is to be applied so that its trailing end will also terminate at the top wall of the evaporator. While I have described without showing one commonly known method of spirally wrapping or coiling convolutions of the defroster-heater around walls of an evaporator it is to be understood that other methods may be employed in so far as the finished evaporator-heater-defroster product is concerned. Means is provided to fasten or clamp the ends only of the defroster-heater to the evaporator after it has been coiled therearound and preferably prior to removing the evaporator-heater from its rotatable holding form on the lathe. Before describing these means it is desired to call attention to the fact that end portions of the metal strip 21 are of different cross-sectional contour than that portion intermediate its ends. This for the purpose of facilitating assembly of the resistance wire 23 to strip 21, for providing effective shielding of wire 23, and for properly clamping ends of the strip to the evaporator particularly at the connection with the conductor wires 28 and 29. While the resistance wire 23 is water-proofed by its insulating coating 20 it is desired to retain the shielding means firmly against the insulation 20 but open at certain points along the length thereof so as to permit defrost water to drain from between the insulated wire and its pocket or shields. It will be noted that the rolled over edges 22 of strip 21 intermediate its end portions are bent to substantially surround the insulated wire 23 (see Figure 3) and its end portion, where wire 23 is curved or looped, is not so bent (see Figure 10) to permit extension of the Wire loop 27 from one side of strip 21 without fracturing the insulation 20. It should also be noted (see Figure 8) that the rolled over edge 22 of strip 21 at the connection between wires 28 and 29 and wire 23 is enlarged to receive and shield the heavier insulated conductor wires 28 and 29. The means for fastening the ends of strip 21 containing the looped portion of wire 23 includes a bracket 36 having a flat body portion secured to the top wall of evaporator 14, by rivets 37, and a raised ear-like portion 38 provided with an elongated opening 39. This means also includes a separate strap 41 which is slit at two spacedapart points and has the metal of the slits bent therefrom to provide same with angularly disposed attaching hooks or tabs 42. The strap 41 is placed over the end of strip 21 with its tabs 42 inserted into two adjacent holes 31 in the strip. An end 43 of strap 41, opposite the end having the integral tabs or hooks 42 thereon, is drawn through the opening 39 and bent over the raised ear 38 on bracket 36. Strap 41 thereby ties the one end of strip 21 to bracket 36 and secures same in contact with the evaporator 14 to prevent it from unraveling, unwrapping or uncoiling from the evaporator. This operation is done by the fingers of a persons hand requiring no special tools and may be carried out just prior to coiling the defroster-heater upon the evaporator or after the evaporator has been removed from a lathe. The means for fastening the opposite end of strip 21, from which the wires 28 and 29 extend, to evaporator 14 includes a bracket 46 secured by rivets 47 to the top Wall of the evaporator and shaped to space a part thereof from the evaporator wall. This opposite end of strip 21 is located over bracket 46 and a clamp 48 is placed thereover. Clamp 48 is drawn down taut, by screws 49, against the rolled over edges 22 of strip 21 in the vicinity of the connection between wire 23 and the conductor wires 28 and 29 to thereby secure the opposite end of strip 21 to the top wall of evaporator 14 to prevent this end of the strip from unwrapping or uncoiling. By coiling flexible strip 21 around walls of the box-like sheet metal evaporator 14 and by fastening its ends thereto the defroster-heater cannot slip relative to the evaporator and is tightly wrapped in metal to metal contact therein whereby to eliminate the necessity of employing a plurality of clamping clips along its length.

When frost or ice builds up on walls of evaporator 14 and on'the defroster-heater wrapped therearound it is desired to melt same therefrom. As before stated a defrosting period may be initiated manually or by some automatic means responsive to a lapse of time or to a predetermined thickness of frost or ice on the evaporator In either event when the resistance wire 23 of the defroster-heater is energized it generates a large amount of heat and dissipates the heat through insulation 20 and uniformly through the flat fin portion of metal strip 21 to wall surfaces of the evaporator 14 to melt frost and ice therefrom which defrost water drains into the tray 13. The spiral coiling of the defroster-heater causes the fin or flat portion of strip 21 to overlap and contact different or adjacent flat walled refrigerant ducts 18 in the sheet metal evaporator and this greatly assists in preventing hot spots along surfaces of the evaporator and in speeding up the defrosting operation. The defrost water is free to flow out of the sheath portions of strip 21 and is by virtue of the holes 31 therein also free to flow outwardly of spaces between walls of the evaporator 14 and the fiat fin portions of the strip intermediate the ducts 18. After defrosting of evaporator 14 has been completed the water in tray 13 should be emptied therefrom before the refrigerating system is again operated. Provision may, if desired, be made to drain the defrost water out of the food compartment as is conventional in the art.

In view of the foregoing it should be apparent to those skilled in the art that I have provided a novel defrosterheater and an improved arrangement for securing same to an evaporator of a refrigerating system. By spirally coiling convolutions of the strip defroster-heater with integral fin means thereon in metal to metal contact with different ones of the refrigerant expansion ducts in walls of the evaporator and from end to end of the evaporator heat is uniformly distributed to the evaporator and to refrigerant therein so as to prevent localized hot spots and provide more efficient defrosting thereof. The particular defroster-heater herein disclosed can be wrapped around and secured to walls of an evaporator without 6 difiiculty and at low manufacturing cost. Flat portions of the strip heater provide same with continuous integral heat dissipating fin means and the fastening of ends only ofthe heater to the evaporator eliminates the necessity of fastening same thereto at a plurality of spaced apart points along convolutions of the defroster-heater.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. In a refrigerator having a refrigerant evaporating element shaped to form walls of a compartment on which frost accumulates, means for melting the frost from said element, said means including a defroster-heater comprising a flexible metallic strip having convolutions thereof spirally coiled around walls of said element and including a rolled over edge portion at least partially surrounding an insulated electrical resistance wire and a flat portion extending tangentially from said rolled over portion forming a heat dissipating fin for said defrosterheater, and said fin contacting walls of said element.

2. The structure defined in claim 1 wherein the ends only of the metal strip are fastened to the element for preventing the defroster-heater from uncoiling from the element.

3. The structure defined in claim 1 wherein the flat fin portion of the metal strip is provided with spaced apart apertures for the drainage of defrost water from walls of the element.

4. In combination, a box-like sheet metal evaporator of a refrigerating system provided with refrigerant ducts along walls thereof, a defroster-heater for said evaporator comprising a flexible substantially flat metallic strip having at least one of its edges rolled over forming a pocket therealong partially enclosing an insulated electrical resistance wire, and said defroster-heater strip having convolutions wound in one direction around walls of said evaporator substantially from end to end thereof with a flat portion of said strip in metal to metal contact with wall surfaces of said refrigerant ducts.

5. The combination defined by claim 4 wherein the ends only of the metal strip are fastened to the evaporator r for preventing unwinding of the defroster-heater there from.

6. The combination defined by claim 4 wherein the flat portion of the metal strip is apertured throughout its length.

7. In combination, an evaporator of a refrigerating system including bonded together metal sheets bent to form a compartment and provided with a plurality of substantially fiat walled refrigerant ducts therebetween extending along said compartment, a defroster-heater for said evaporator comprising a flexible metallic strip having a flat portion with one of its edges rolled over an insulated electrical resistance wire to provide a sheath therefor, said strip being spirally coiled around said evaporator and having its ends fastened thereto for preventing uncoiling thereof therefrom, and said fiat portion in metal to metal contact with said flat walled refrigerant ducts of said evaporator.

8. The combination defined by claim 7 wherein the flat portion of the metal strip is provided with spaced apart apertures at least along a part of the length thereof.

9. In combination, an evaporator of a refrigerating system including bonded together metal sheets bent to form a compartment and provided with a plurality of substantially fiat walled refrigerant ducts therebetween extending along said compartment, a defroster-heater for said evaporator comprising a substantially fiat metallic strip and an elongated U-shaped insulated electrical re sistance wire carried thereby, the edges of said metallic strip being rolled over legs of said U-shaped wire and providing a sheath therefor, said defroster-heater being spirally wound around opposed walls of said evaporator substantially from end .to end thereof with the flat portion of said strip in metal to metal contact with said fiat walled refrigerant ducts, and means for fastening the ends only of said metallic strip to the evaporator to prevent uncoiling of the defroster-heater therefrom.

10. The combination defined by claim 9 wherein at least a part of the length of the flat portion of the metallic strip is apertured.

7 11. The combination defined by claim 9 wherein a convolution of the spirally wound defroster-heater overlaps different ones of the refrigerantducts.

12. In a refrigerator, anevaporator including bonded together metal sheets provided with fiat walled refrigerant ducts therebetween, a defroster-heater for said evaporator comprising a metallic strip having a rolled over edge at least partially surrounding an insulated electrical resistance wire and an integral flat part projecting tangentially fromsaid rolled over edge, said flat part of said strip providing said defroster-heater with a heat dissipating fin substantially coextensivetherewith, and means for securing said defroster-heater to said evaporator with said fin overlying and being in metal-to-metal contact withsaid flat walled refrigerant ducts throughout the width of portions thereof.

13. The structure defined by claim 12 wherein the fiat part of the metallic strip is apertured along at least portions of its length for passage of defrost water therethrough from,the evaporator. I

. 14. In are'frigerator having a refrigerant evaporating element shaped to form walls 'ofa compartment on which frostaccumulates, means foimelting the frost from said element, said means including a defroster-heater comprising a flexible'met'allic strip having convolutions thereof woundinv onedirection around walls of said element and including a sheathportion at least partially surrounding an insulated electrical resistance wire and an integral flat portion projecting from said sheath portion, said flat portion of said strip providing said defroster-heater with a heat dissipatingfindisposed in contact with walls of said element, and the ends only of said metallic strip being fastened to saidelement for preventing unwinding of the defroster-heater therefrom. g

15. The structure defined in claim 14 wherein the flat portion of the metal strip is apertured for the drainage of defrost water from walls of the element.

16. The structure defined inclaim 14 wherein the fin is coextensive with the length of the sheath.

Snlzberger Dec. 17, 1935 Duncan et al. June 12, 1956 

